Bidirectional data pin, clock input pin, shift register, debug circuitry

ABSTRACT

A two pin communication interface bus and control circuits are used with circuit boards, integrated circuits, or embedded cores within integrated circuits. One pin carries data bi-directionally and address and instruction information from a controller to a selected port. The other pin carries a clock signal from the controller to a target port or ports in or on the desired circuit or circuits. The bus may be used for serial access to circuits where the availability of pins on ICs or terminals on cores is minimal. The bus is used for communication, such as serial communication related to the functional operation of an IC or core design, or serial communication related to test, emulation, debug, and/or trace operations of an IC or core design.

This application is a divisional of prior application Ser. No.16/003,780, filed Jun. 8, 2018, now U.S. Pat. No. 10,522,200, issuedDec. 31, 2019;

Which was a divisional of prior application Ser. No. 15/270,673, filedSep. 20, 2016, now U.S. Pat. No. 10,020,032, granted Jul. 10, 2018;

Which was a divisional of prior application Ser. No. 14/148,031, filedJan. 6, 2014, now U.S. Pat. No. 9,477,626, granted Oct. 25, 2016;

Which was a divisional of prior application Ser. No. 13/785,133, filedMar. 5, 2013, now abandoned;

Which was a divisional of prior application Ser. No. 11/258,315, filedOct. 25, 2005, now U.S. Pat. No. 8,412,853, granted Apr. 2, 2013;

Which claims the benefit of prior application 60/622,255, filed Oct. 25,2004.

BACKGROUND OF THE INVENTION Technical Field

This description pertains generally to serial communications andparticularly to providing a serial communications interface between acontroller and a selected communications port.

Brief Description of Related Art

Semiconductor manufacturing test and other operations such as trace,debug, and emulation often use the interface signals defined in IEEEStandard 1149.1, commonly known as JTAG. This interface defines four tofive leads used to send and receive serial data to and from a targetcircuit. This interface is broadly used in the industry today and hasbeen extended beyond its original purpose of boundary scan.

The number of pins available for such serial communication to and from atarget circuit is being reduced because of package size reductions thatrequire most of the pins to be used for functional purposes.

Thus a need has arisen for a reduced pin interface to and from a targetcircuit. While such an interface can be used in semiconductormanufacturing test and other operations such as trace, debug andemulation, such an interface could also be used generally for othertypes of serial communication.

BRIEF SUMMARY OF THE INVENTION

This disclosure pertains to a communications interface using one wire orpin for data transmission and one wire or pin for a clock signaltransmission between the controller and selected data port. Thiscommunications interface finds utility in an external controllercommunicating with internal registers, such as boundary scan, serialscan, test, trace, debug, and functional registers of such as anintegrated circuit, core circuits in an integrated circuit, or corecircuits within core circuits in an integrated circuit.

The serial data communications circuit comprises a bi-directionalexternal data signal lead and an external clock signal input lead. DataI/O circuitry is connected to the bi-directional external data signallead and provides an internal input data signal lead and an internaloutput data signal lead.

Port controller circuitry has an input connected to the external clocksignal input lead and has an input connected to the internal input datasignal lead to control operation of the port. Instruction circuitry andaddress circuitry are connected to the internal input data signal leadand to the port controller circuitry to provide control information tothe port controller. The port controller circuitry includes a statemachine operating in response to the external clock signal and signalsfrom the address circuitry.

Data circuits are connected to the internal input data signal lead andto the port controller circuitry. The data circuits can be one or moreof functional circuits, boundary scan circuits, serial scan circuits,test circuits, trace circuits, debug circuits, and emulation circuits.

The data I/O circuitry includes comparator circuitry determining thelogic state of data received on the external bi-directional data signallead in response to the logic state of data on the internal output datasignal lead. The data I/O circuitry also includes multiplexer circuitryto output a data signal on the internal data signal lead in response tothe data signal detected on the external bi-directional data signal leadby the comparator circuitry.

A system can include the port circuit and a bus controller connected tothe bi-directional external data signal lead and to the external clocksignal input lead. The bus controller supplies the clock signal to theserial data communications circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the two pin bus interface circuit.

FIG. 2 illustrates two communication messaging operations of the two pinport.

FIG. 3 illustrates two pin bus targets interfaced to a two pin buscontroller.

FIG. 3A illustrates the controller realized by an interface card in apersonal computer with a cable connection.

FIG. 4 illustrates the two pin port of FIG. 1 in more detail.

FIG. 5 illustrates the port controller of FIG. 4 in more detail.

FIG. 6 illustrates the frame bit counter circuit in more detail.

FIG. 7 illustrates the state diagrams of the port and message resetcontroller and the message controller.

FIGS. 8A and 8B illustrate an example implementation of controller ofFIG. 5.

FIG. 9 illustrates an example implementation of the message controllerstate machine of FIG. 8.

FIG. 10 illustrates an example implementation of the address circuit ofFIG. 1.

FIG. 11 illustrates an example implementation of the instruction circuitof FIG. 1.

FIG. 12 illustrates in general an example implementation of datacircuits within the data circuit block of FIG. 1.

FIG. 13 illustrates the data circuits block of FIG. 1.

FIG. 14 illustrates a data circuit as an internal scan register coupledto combination logic.

FIG. 15 illustrates a data circuit as a boundary scan register coupledto the device's (IC or core) I/O terminals.

FIG. 16 illustrates a data circuit as a data register.

FIG. 16A illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as an destination input circuit.

FIG. 16B illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as a source output circuit.

FIG. 16C illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as both a source output circuitand as a destination input circuit.

FIG. 16D illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as an destination input circuit.

FIG. 16E illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as a source output circuit.

FIG. 16F illustrates the data register realized as the shift register ofFIG. 12, and the I/O circuit realized as both a source output circuitand as a destination input circuit.

FIG. 16G illustrates an example data circuit design for providing theshift register of a data register to address one of four addressable I/Oregisters 1-4 existing as the general I/O circuitry of FIG. 16 and writeand/or read data to the addressed I/O register.

FIG. 17 illustrates an example implementation of the port and messagereset controller.

FIG. 18 illustrates a timing diagram.

FIG. 19 illustrates a timing diagram.

FIG. 20 illustrates a timing diagram.

FIG. 21 illustrates a timing diagram.

FIG. 22 illustrates a timing diagram.

FIG. 23 illustrates a timing diagram.

FIG. 24 illustrates a timing diagram.

FIG. 25 illustrates the data signal wire connection between the data I/Ocircuit of a port controller and data I/O circuits of 1-N targetcircuits.

FIG. 26 illustrates one example implementation of the data input circuitof the data I/O circuits.

FIG. 27A illustrates the case where the port controller output bufferand target port output buffer are both outputting logic lows to datasignal wire.

FIG. 27B illustrates the case where the port controller output buffer isoutputting a low on data signal wire and target port output buffer isoutputting a high on data signal wire.

FIG. 27C illustrates the case where the port controller output buffer isoutputting a high on data signal wire and target port output buffer isoutputting a low on data signal wire.

FIG. 27D illustrates the case where the port controller output bufferand target port output buffer 406 are both outputting logic highs todata signal wire.

FIG. 28 illustrates timing waveforms.

FIG. 29 illustrates an example implementation of the two pin port in adevice (IC or core) extended to include auxiliary data signals toincrease the data input and output bandwidth between the device and anexternal port controller.

FIG. 30 illustrates the IC or core device wherein the data circuitsselected by an instruction for a parallel data I/O operation are scanregisters 1-N used for testing.

FIG. 31 illustrates the IC or core device wherein the data circuits ofFIG. 30 selected by an instruction for a parallel data I/O operation arecircuits 1-N used for debug or trace operations.

FIG. 32 illustrates the IC or core device wherein the data circuitsselected by an instruction for a parallel data I/O operation arefunctional circuits 1-N of the device.

DESCRIPTION OF THE DISCLOSED EMBODIMENTS

FIG. 1 illustrates the 2 pin bus interface circuit 102. As seen the 2pin interface circuit includes an external data lead 104 and clocksignal lead 106, both of which are coupled to a 2 pin port 108 withinthe interface circuit architecture. The data and clock signals includepull up elements 116 to maintain a logic high on the signals wheneverthey are not externally driven.

The 2 pin port is further coupled to an address circuit 110, instructioncircuit 112, and a data circuit 114. The address circuit is controlledby the 2 pin port to input serial data from the data signal lead, viathe 2 pin port's In 118 output lead, in response to address control (AC)output 122 from the 2 pin port. The address circuit outputs an addressmatch signal 124 to the 2 pin port. The address match signal indicateswhether the address input to the address circuit matches the address ofthe 2 pin port. If the address matches, the port is selected for furthercommunication, otherwise the port is not selected for furthercommunication.

The instruction circuit is controlled by the 2 pin port to input serialdata from the data signal, via the In 118 output, in response toinstruction control (IC) output 126 from the 2 pin port. The instructioncircuit outputs instruction output 128 to the 2 pin port, the datacircuits, and optionally to other circuits external of the 2 pin busarchitecture. The instruction output to the 2 pin port regulates theport's data control (DC) outputs 130 to the data circuits. Theinstruction output to the data circuits selects one of a plurality ofdata circuits for access. The instruction circuit receives a port resetsignal 132 from the 2 pin port which, if active, initializes theinstruction circuit to a desired instruction.

The data circuits are controlled by the 2 pin port to simultaneouslyinput and output data via the data signal in response to data control(DC) output 130 from the 2 pin port. The input data to the data circuitscomes from the In output 118 of the 2 pin port and the output data fromthe data circuits is input to the Out 120 input of the 2 pin port. The 2pin port is optionally coupled to a function reset signal 134 within theIC or core such that it may be reset whenever the IC or core functionalcircuits are reset, say at power up of the IC or core. When the 2 pinport is reset by the function reset, the instruction circuit is alsoreset via the port reset signal 132.

FIG. 2 illustrates two communication messaging operations of the 2 pinport. The top message operation 202 shows the 2 pin port exiting theport reset state 204, entering the message reset state 204, performingan address input 208 to address the port, performing an instructioninput 210 to instruct the port, then returning to the message resetstate 206. From the message reset state 206 the address and instructionmessage input can be repeated as indicated by the loop back line, or the2 pin port can re-enter the port reset state 204. The message resetstate 206 resets the 2 pin port but does not reset the instructioncircuit via the port reset signal 132. The port reset state 204 resetsthe 2 pin port and also resets the instruction circuit via the portreset signal 132. Message operation 202 is used to address a port andinput an instruction to the addressed port.

The bottom message operation 214 shows the 2 pin port exiting the portreset state 204, entering the message reset state 206, performing anaddress input 208 to address the port, performing an instruction input210 to instruct the port, performing a data input and output 212 towrite and read data from a data circuit coupled to the port, thenreturning to the message reset state 206. From the message reset state206 the address input, instruction input, and data input/output messagecan be repeated as indicated by the loop back line, or the 2 pin portcan re-enter the port reset state 204. Message operation 214 is used toaddress a port, input an instruction to the addressed port, andcommunicate data bi-directionally to a data circuit coupled to the port.

FIG. 3 illustrates 2 pin bus targets interfaced to a 2 pin buscontroller 302. The targets may be ICs (or die) 310 on a board or othersubstrate 304, cores 312 embedded within ICs 306, or cores 314 embeddedwithin cores 312. Each target has a unique address to provide it to beindividually selected by the controller 302 for serial messagecommunication independent of the target's physical or hierarchicallocation in the system (board/IC/core) in which it resides. Bytransmitting the target address, the controller 302 can input aninstruction as shown in message operation 202, or can input aninstruction followed by performing a data I/O operation as shown inmessage operation 214. In addition to having a unique address, eachtarget port contains a global address that provides the controller toaddress all the targets simultaneously so that all the targets may beloaded with an instruction. The global address and instruction inputuses message operation 214.

FIG. 3A is provided to indicate that the controller 302 may be realizedby using an interface card 316 in a personal computer 318 to control theclock and data signal communication to the 2 pin bus targets 310-314 viaa cable connection 320.

FIG. 4 illustrates the 2 pin port 108 of FIG. 1 in more detail. The 2pin port includes a data I/O circuit 402 and a port controller circuit418. The data I/O circuit 402 includes an output buffer 406, a resistor404, and a data input circuit 408. The output buffer 406 has an inputcoupled to the Out signal 120 from data circuits 114, an output coupledto one lead of resistor 404, and a 3-state control input coupled to anoutput enable signal 416 from port controller 418. The other lead ofresistor 404 is coupled to data signal lead 104.

The data input circuit 408 has a first input coupled to the data signallead 104 on lead 412, a second input coupled to the Out signal 120 onlead 414, and an output coupled to In signal 118 to the address,instruction, and data circuits 110-114. If the output enable signal 416is inactive low, the output buffer 406 is disabled and the data inputcircuit 408 operates as a conventional 2-state input buffer. That is tosay, when the output enable is low, the data input circuit inputs2-state data from data signal 104 and outputs corresponding 2-state datato In signal 118. If the output enable signal 416 is active high, theoutput buffer 406 is enabled and the data input circuit 408 operates toevaluate the voltages present at its inputs 412 and 414 and to output anappropriate 2-state signal, based on the evaluation, to In signal 118.

FIG. 5 illustrates the port controller 418 of FIG. 4 in more detail. Theport controller consists of a port and message reset controller 502, amessage controller 504, and a frame bit counter circuit 506. The port &reset controller contains two controllers, a port reset controller and amessage reset controller. The port reset controller outputs a messagereset signal 508 to reset the message controller 504 and instructioncircuit 112 when a port reset sequence is applied on the clock 106 anddata 104 (via In signal 118) signals, or in response to a functionalreset signal 134. The message reset controller outputs a port resetsignal 132 to reset the message controller 504 at the end of eachmessage transaction to provide the message controller to be setup forsubsequent message transactions.

The message controller 504 outputs an address clock (A-Clock) signal 510to shift an address into the address circuit from the In 118. Themessage controller outputs an instruction clock (I-Clock) signal 512 toshift an instruction into the instruction circuit from the In signal 118and an instruction update (I-Update) signal 514 to update theinstruction shifted into the instruction circuit to the instructionoutput bus 128. The message controller outputs a number of data clocks(D-Clock1-N) signals 516, a number of data capture (D-Capture) signals518, and a number of data update (D-Update) signals 520. The D-Clock1-N,D-Capture1-N, and D-Update1-N signals are each associated with a datacircuit 1-N, such that a data circuit 1 inputs D-Clock1, D-Capture1,D-Update1, a data circuit 2 inputs D-Clock2, D-Capture2, D-Update2, andso on. The D-Clock signal clocks the data circuit during serial shiftand parallel capture operations. The D-Capture signal regulates theshift and capture operations of the data circuit. The D-Update signalcause data shifted into the data circuit to be updated (i.e. output) tothe parallel outputs of the data circuit. The message controller outputsan output enable signal 416 to the data I/O circuit 402, a shift datastate indication signal 522, a counter clock signal 524, and a counterreset signal 526 to the frame bit counter circuit 506.

The message controller inputs the message reset signal 508 fromcontroller 502, the external clock signal 106, the In signal 118 fromdata I/O circuit 402, the address match signal 124 from address circuit110, instruction output signals 128 from instruction circuit 112, and acount complete signal 528 from the counter 506.

FIG. 6 illustrates the frame bit counter circuit 506 in more detail.Counter circuit 506 includes a counter 608, a comparator 606, a countlimit multiplexer 604, and count limit select circuit 610. The countercircuit outputs a count complete signal 528 to the message controller.The counter circuit inputs data limit select A and B signals frominstruction output bus 128 and shift data state indication signal 522,counter clock signal 524, and counter reset signal 526 from the messagecontroller 504. The select A and B inputs provide for selectingdifferent length shift operations to data circuits 114 by selecting acount limit 614-616 which differs from the common count limit 612 usedby the address and instruction circuits. If the select A and B signals128 are low or if the shift data state indication signal 522 is low, thecount limit select circuit 610 will select the common count limit 612 tobe input to the comparator. If the shift data state indication signal522 is high, the values input on the select A and B inputs willdetermine the count limit 612-616 to be input to the comparator.

For example, if A:B=0:0 the common count limit 612 is input, if A:B=0:1a data count limit 1 614 is input, if A:B=10 a data count limit 2, whilenot shown, is input, and if A:B=1:1 a data count limit 3 616 is input.While two select signals (A and B) are shown to select one of four countlimits, any number may be used to select any number of count limits tothe comparator 606. The count limit select circuit 610 may be modifiedas required for more or less count limit select inputs 128 from theinstruction register and to correspondingly output more or less selectcontrol inputs 618 to the count limit multiplexer 604.

Prior to performing a shift operation to the address, instruction, ordata circuits the counter 608 will be reset to a count of zero. Eachtime a data bit is shifted into the one of the address, instruction, ordata circuits the counter increments. The count output from the counteris input to the comparator along with the count limit from the countlimit multiplexer 604. When the count output matches the count limit thecomparator outputs a count complete signal 528 to the message controller504. In response to the count complete signal being set, the messagecontroller will cease the shift operation and perform a next operation.

The shift path lengths of the address circuit 110 and instructioncircuit 112 are the same. For example they may both be 16 bits long.During address and instruction shift operations the A and B inputs tothe count limit multiplexer 604 will be set to select the common countlimit 612 to be input to the comparator. The common count limit 612 forthe example 16 bit shift will be a count of 16. If a data circuit shiftpath length is also 16 bits, the common count limit of 16 can be usedfor shifting the data circuit as well. However, if a data circuit has ashorter or longer shift path length than 16, the select A and B inputsenable a different count limit to be used for the data circuit.

For example, if a data circuit has a shift path of 512 bits, a datacount limit of 512 will provided and selected by the count limitmultiplexer to be input to the comparator. If the shift path length ofanother data circuit is 256 bits long, a data count limit of 256 will beprovided and selected by the count limit multiplexer for input to thecomparator. The ability to use the select A and B inputs to selectdifferent count limits 612-616 is only available during times when themessage controller 504 is shifting data through a data circuit, i.e.when the shift data state indicator signal 522 is high. During theaddress and instruction shift operations, the shift data state indicator522 will be low which forces the common count limit 612 to be used,independent of the select A and B inputs.

FIG. 7 illustrates the state diagrams of the port and message resetcontroller 502 and the message controller 504. Following a functionalreset or in response to a port reset sequence (PRS), the port & messagereset controller will be in the port reset state 706. The port resetsignal 132 and message reset signals 508 are active low while the port &message reset controller 502 is in the port reset state. In response toa message reset sequence (MRS) the port & message reset controller willbe in the message reset state 708. The message reset signal 508 isactive low while the port & message reset controller 502 is in themessage reset state 708.

A message may be initiated by transitioning from the message reset state708 of the port & message reset controller to the shift address state710 of the message controller. The message controller remains in theaddress shift state 710 shifting address bits into the address circuituntil the count complete (CC) signal from counter circuit 506 goes high.From the address shift state 710 the message controller transitions tothe address match state 712 to test for a match between the addressshifted in and the 2 pin port's address and to reset the counter 608 viathe counter reset signal 526. If the address does not match, the messagecontroller transitions to the port idle state 724 and remains thereuntil a message reset sequence (MRS) occurs.

If the address matches, the message controller transitions to the shiftinstruction state 714 to shift in an instruction. When the countcomplete (CC) signal goes high, the message controller transitions tothe update instruction state 716 to update the instruction to theinstruction output bus 128 and to reset the counter 608 via the counterreset signal 526. If a message reset sequence (MRS) occurs during theupdate instruction state 716, the message controller transitions fromthe update instruction state 716 to the message reset state 708 of theport & message reset controller 502 to terminate the message.

If the message terminates from the update instruction state 716, themessage is an address and instruction message as illustrated inmessaging operation 202 of FIG. 2. If a message reset sequence (MRS)does not occur during the update instruction state 716, the messagecontroller transitions to the capture data state 718. In the capturedata state 718 the parallel inputs of the data circuit 114 selected bythe loaded instruction are captured in the data circuit. From thecapture data state 718 the message controller transitions to the shiftdata state 720. During the shift data state, the output enable signal416 to the data I/O circuit 402 is set high, which enables the data I/Ocircuit 402 to simultaneously input and output data on data signal 104,as mentioned in regard to FIG. 4. Also during the shift data state, theselected data circuit 114 shifts data in from the In signal 118 outputof data I/O circuit 402 and shifts data out to the Out signal 120 inputof data I/O circuit 402.

When the count complete (CC) signal goes high, the message controllertransition from the shift data state 720 to the update data state 722.During the update data state, the selected data circuit outputs the datashifted in, resets the counter 608 via counter reset signal 526, andsets the output enable signal 416 back low. If a message reset sequence(MRS) occurs during the update data state 722, the message controllertransitions from the update data state 722 to the message reset state708 of the port & message reset controller 502 to terminate the message.If the message terminates from the data update state 722, the message isan address, instruction, and data message as illustrated in messagingoperation 214 of FIG. 2. If a message reset sequence (MRS) does notoccur during the update data state 722, the message controllertransitions to the capture data state 718 to repeat the above mentioneddata capture, shift, and update operation steps. The data capture,shift, and update operation steps can be repeated as necessary toachieve a desired number of data input and output operations associatedwith a test, debug, trace, emulation, or other support or functionalinput/output operation required in the IC or core in which the 2 pin busis implemented.

From the above description, it is clear that address circuit andinstruction circuit input operations occur while the output enablesignal 416 is low, which makes the data I/O circuit 402 operate as a 2state input buffer whereby data may be transferred uni-directionallyfrom a 2 pin bus controller 302 to the a 2 pin bus target as shown inFIG. 3A via the data signal 104. It is also clear that data circuitinput/output operations occur while the output enable signal 416 ishigh, making the data I/O circuit 402 operate in its input and outputmode whereby the data is simultaneously transferred bi-directionallybetween the 2 pin bus controller 302 and a 2 pin bus target of FIG. 3Avia the data signal 104. These two modes of the data I/O circuit 402were described previously in regard to FIG. 4.

FIGS. 8A and 8B illustrate an example of how the message controller 504of FIG. 5 may be designed. The message controller consists of a messagecontroller state machine 802 having output leads carrying signalsindicating when the state machine is in certain states. These leads arethe shift address state lead 816, shift instruction state lead 818,update instruction state lead 820, shift data state lead 822, updatedata state lead 824, capture data state lead 826, and address matchstate lead 828. The message controller 504 also includes flip flops836-852, and various And, Or, an inverter gating circuits. The statemachine 802 responds to the rising edge of clock signal 106 and the flipflops 836-852 respond to the falling edge of the clock signal 106. Thistiming provides for glitch free gating of clock and control outputsignals from the message controller 504.

While the message reset input 508 is low, the state machine is forced toand remains in the shift address state 710 of the state diagram of FIG.7, and the flip flops 836-852 are held in reset. When the message resetinput 508 goes high, the reset condition on the state machine and flipflops is removed and the state machine operates as described in regardto the state diagram of FIG. 7. While the state machine is in the shiftaddress state, the A-Clock signal 510 will be gated on to output clocksignals 106 to the address circuit 110. While the state machine is inthe shift instruction state, the I-Clock signal 512 will be gated on tooutput clock signals 106 to the instruction circuit 112. While the statemachine is in the update instruction state, the I-Update signal 514 willbe gated on to update the outputs of the instruction circuit

While the state machine is in the shift data state, the D-Clock signal804 will be gated on to output clock signals 106 to the selected datacircuit 114. While the state machine is in the update data state, theD-Update signal 806 will be gated on to update the output of theselected data circuit. While the state machine is in the data capturestate, the D-Capture signal 808 and D-Clock signal 804 will be gated onto cause the selected data circuit to capture data. The counter clocksignal 524 will be gated on whenever the state machine is in the shiftaddress, shift instruction, or shift data state. The counter resetsignal 526 will be gated on whenever the state machine is in the updateinstruction, update data, or address match state, or when the messagereset signal is low. The output enable signal 416 will be gated onwhenever the state machine is in the shift data state. The shift datastate indication signal 522 will be gated on whenever the state machineis in the shift data state.

In FIG. 8B the D-Clock signal 804 is input to gating circuits 864, theD-Capture signal 808 is input to the gating circuits 866, and theD-Update signal 806 is input to the gating circuits 868. Instructionoutput bus signals 810, 812, and 814 are input to the gating circuits864, 866, and 868. If instruction signal 810 is high, the D-Clock signaloutputs to the D-Clock1 signal of 516, the D-Capture signal 808 outputsto D-Capture1 signal of 518, and D-Update signal 806 outputs toD-Update1 signal of 520. If instruction signal 812 is high, the D-Clocksignal outputs to the D-Clock2 signal of 516, the D-Capture signal 808outputs to D-Capture2 signal of 518, and D-Update signal 806 outputs toD-Update2 signal of 520. If instruction signal 814 is high, the D-Clocksignal outputs to the D-ClockN signal of 516, the D-Capture signal 808outputs to D-CaptureN signal of 518, and D-Update signal 806 outputs toD-UpdateN signal of 520. Thus instruction output signals 810-814selectively direct the D-Clock 804, D-Update 806, and D-Capture 808output signals to the selected data circuits 114 1-N, respectively.

FIG. 9 illustrates an example of how the message controller statemachine 802 of FIG. 8 may be designed. The state machine consists ofnext state decode logic 902, state flip flops A, B, C 904-908, andoutput state decode logic 910-924. If the message reset input 508 islow, the state machine is reset to the shift address state 816,(ABC=000). If the message reset input is high, the state machineresponds to the rising edge of the clock input 106 to transition throughits states according to the In 118, address match 124, and countcomplete 528 inputs shown in state diagram 704 of FIG. 7. The A,B,Cstate assignments are shown in box 926. The output state decode logic910-924 provides the signals shown in FIG. 8 on the shift address statelead 816, address match state lead 828, shift instruction state lead818, update instruction state lead 820, shift data state lead 822,update data state lead 824, and capture data state lead 826. The portidle state signal on lead 928 is also shown being decoded in the eventit is needed for indicating when the port is in the idle state.

FIG. 10 illustrates an example of how the address circuit 110 of FIG. 1may be designed. The address circuit consists of an address shiftregister 1012, an address compare circuit 1014, and a port addresscircuit 1016. The shift register 1012 responds to A-Clock 510 inputs toshift in an address from the In 118 input. The compare circuit 1014operates to compare the address shifted into the shift register 1012 tothe address in the port address circuit 1016. The compare circuitoutputs the result of the compare on the address match signal 124. Theport address in circuit 1016 may be a hardwired address, an addressprovided by the blowing of electronic fuses, an address programmed intoa programmable memory, an address functionally written into a memory, anaddress shifted into a shift register, or by any other suitable addresssupplying means.

In addition to the port's individual address, the port address circuit1016 also contains the global address mentioned in regard to FIG. 3. Theglobal address is the same for all 2 pin ports, which enables all portsto addressed at the same time for inputting an instruction to all theports using message 202 of FIG. 2. The global address must not be usedby any port as an individual port address. The compare circuit iscapable of comparing the data shifted into the address register 1012against both the individual port address and the global port addressoutput from port address circuit 1016. If a match occurs between thedata in the address register 1012 and the individual or global portaddress, the address match signal 124 will be set high.

FIG. 11 illustrates an example of how the instruction circuit 112 ofFIG. 1 may be designed. The instruction circuit consists of aninstruction shift register 1112, instruction decode logic 1114, and aninstruction update register 1116. The shift register 1112 responds toI-Clock 512 inputs to shift in an instruction from the In 118 input. Thedecode logic 1114 operates to decode the instruction shifted into theshift register 1112 and to output the decode to the update register1116. The update register 1116 stores the instruction decode in responseto the I-Update signal 514. The stored instruction decode is output fromthe update register to the instruction output bus 128. The port resetsignal 132 is input to both the shift register 1112 and update register1116 to reset the registers to known states when the port reset signalis active low.

FIG. 12 illustrates in general an example of how data circuits 1212within data circuit block 114 of FIG. 1 may be designed. Each datacircuit will consist of a data register 1214 having a serial inputcoupled to the In 118 signal, a serial data output coupled to the Out120 signal, and parallel inputs and parallel outputs coupled to a sourceand/or destination circuit 1216. A data register 1214 may have onlyparallel inputs from a source circuit, only parallel outputs to adestination circuit, or both parallel inputs from a source circuit andparallel outputs to a destination circuit. The source and destinationcircuits may be part of the data circuit 1212 or they may be separatecircuits coupled to the data circuit 1212. In data register circuit1222, it is seen that a data register 1214 may include only a shiftregister 1218 that is coupled serially to the In and Out signals and inparallel to the source and/or destination circuits. In data registercircuit 1224, it is seen that a data register 1214 may additionallyinclude an update register 1220 between the parallel outputs of theshift register 1218 and the parallel inputs of the destination circuit.

If the D-Capture signal 518 is high, the shift register 1218 capturesparallel data from a connected source in response to the D-Clock signal516. If the D-Capture signal 518 is low, the shift register 1218 shiftsdata from the In 118 signal to the Out 120 signal in response to theD-Clock signal 516. At the end of the shift operation, the updateregister 1220, if implemented as shown in 1224, stores the paralleloutputs from the shift register 1218 in response to the D-Update signal520 and outputs the stored parallel outputs to a destination circuit. Ifan update register 1220 is not implemented, as shown in 1222, theparallel outputs from the shift register 1218 are input directly to thedestination circuit. As seen in the data circuit 1212 of FIG. 12, theD-Update signal 520, D-Capture signal 518, and D-Clock signal 516 may beinput to the source and/or destination circuits. The D-Update signal canbe used to directly control or indicate when the destination circuitshould input parallel data from the data register 1214. The D-Capturesignal can be used to directly control or indicate when the sourcecircuit should output parallel data to the data register 1214. TheD-Clock signal can be used as a clock input to the source and/ordestination circuits to provide the timing for data input and/or outputoperations.

FIG. 13 illustrates the data circuits block 114 of FIG. 1. The datacircuits block consists of 1-N data circuits 1212 a multiplexer 1302,and falling edge triggered flip flop 1312. Data circuit 1 receivesD-Update1, D-Capture1, and D-Clock1 signals from control buses 516-520of DC bus 130. Data circuit 2 receives D-Update2, D-Capture2, andD-Clock2 signals from control buses 516-520 of DC bus 130. Data circuitN receives D-UpdateN, D-CaptureN, and D-ClockN signals from controlbuses 516-520 of DC bus 130. Each data circuit 1-N receives serial inputfrom In signal 118, and each output separate serial outputs 1306-1310 tomultiplexer 1302. Multiplexer 1302 outputs to the Out signal 120, viaflip flop 1312, and receives select input signals from instructionoutput bus 128 to select which data circuit 1212 serial output 1306-1310is coupled to the Out signal 120. Flip flop 1312 is clocked by theD-Clock signal 804.

When an instruction is loaded into the instruction circuit 112 to selectone of the data circuits 112 in data circuits block 114 for a data I/Ooperation, the selected data circuit's serial output will be coupled tothe Out signal 120 via multiplexer 1302 and flip flop 1312 and theappropriate D-Update, D-Capture, and D-Clock signal inputs to the datacircuit from the message controller 504 will be enabled. Once selectedthe data register will capture parallel data input from a source, shiftdata from In signal 118 to Out signal 120, and update parallel dataoutput to a destination. During the capture and shift operations of anyselected data circuit 1212, flip flop 1312 will be clocked by thefalling edge of D-Clock 508 to pass data from multiplexer 1302 to thedata I/O circuit 402 via Out signal 120. While the selected data circuit112 is performing a data I/O operation, the other non-selected datacircuits 1212 of data circuits block 114 will remain inactive. Thefollowing FIGS. 14-16 illustrate three examples of different datacircuit 1212 types.

The data circuit 1402 of FIG. 14 illustrates that a data circuit may bean internal scan register 1404 coupled to combination logic 1406 toprovide scan testing of the combinational logic. During scan testing,the D-Capture and D-Clock signals cause the internal scan register tocapture test response data from the combination logic and to shift theresponse data out to Out signal 120 while the next test stimulus data isshifted into the internal scan register from In signal 118 to be outputto the combination logic. The D-Update signal is typically not requiredduring internal scan testing operations, so it is not shown connected tothe internal scan register 1404. The internal scan register 1404 wouldtypically appear as data register 1222 of FIG. 12. The inputs 1408 tothe combination logic 1406 would be the destination outputs of shiftregister 1218 and the outputs 1410 from the combination logic 1406 wouldbe the source inputs to shift register 1218.

The data circuit 1502 of FIG. 15 illustrates that a data circuit may bea boundary scan register 1504 coupled to the device's (IC or core) I/Oterminals 1506 to provide boundary scan testing at the device I/Oterminals. During boundary scan testing, the D-Capture and D-Clocksignals cause the boundary scan register to capture test response datafrom the device I/O terminals and to shift the response data out to Outsignal 120 while the next test stimulus data is shifted into theboundary scan register from the In signal 118 to be output to the deviceI/O terminals in response to the D-Update signal. The D-Update signal istypically required during boundary scan testing, so it is shownconnected to the boundary scan register 1504. The boundary scan register1504 would typically appear as data register 1224 of FIG. 12. The inputs1508 to the device I/O terminals 1506 would be the destination outputsof update register 1220 and the outputs 1510 from the device I/Oterminals 1506 would be the source inputs to shift register 1218.

The data circuit 1602 of FIG. 16 illustrates that a data circuit may bedata register 1604 for performing general purpose I/O operations totest, debug, trace, functional, or other I/O circuits 1606. During dataI/O operations, the D-Capture and D-Clock signals cause the dataregister to capture data input from I/O circuitry 1606, to shift thecaptured data out to Out signal 120, and to shift input data into thedata register from the In signal 118 to be output to the I/O circuitry1606 in response to the D-Update signal.

The D-Update signal to data register 1604 may or may not be needed fordata I/O operations, so it is shown in dotted line. If the D-Updatesignal is not needed, data register 1604 would appear like circuit 1222of FIG. 12 in that the inputs 1608 to the I/O circuitry 1606 would bethe destination outputs of shift register 1218 of circuit 1222 and theoutputs from the I/O circuitry 1606 would be the source inputs to shiftregister 1218 of circuit 1222. If the D-Update signal is needed, dataregister 104 would appear like circuit 1224 of FIG. 12 in that theinputs 1608 to the I/O circuitry 1606 would be the destination outputsof update register 1220 of circuit 1224 and the outputs from the I/Ocircuitry 1606 would be the source inputs to shift register 1218 ofcircuit 1224.

As mentioned in regard to FIG. 12, the D-Update, D-Capture, and D-Clocksignals may be input to the I/O circuitry 1606 to directly control orindicate when the I/O circuitry should input data from or output data todata register 1604. Following FIGS. 16A-16C illustrate how the D-Update,D-Capture, and D-Clock signals can directly control the I/O circuitry1606. Following FIGS. 16D-16F illustrate how the D-Update, D-Capture,and D-Clock signals can indicate when to control an I/O operation to I/Ocircuitry 1606. Following FIG. 16G illustrates one example of I/Ocircuitry 1606 being directly controlled by the D-Update and D-Clocksignals.

In FIG. 16A, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1606 of datacircuit 1602 is realized as an destination input circuit 1612 forstoring the output 1613 from shift register 1218 in response to theD-Update signal 520. Following the shifting of data into the shiftregister 1218, the D-Update signal will cause the input circuit 1612 toload the data and output the data as input data to another circuit. Asseen in this example, the D-Update signal directly controls the inputcircuit 1612.

In FIG. 16B, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1606 of datacircuit 1602 is realized as a source output circuit 1614 for capturingdata from another circuit in response to the D-Clock and D-Capturesignals and providing the captured data as input 1615 to the shiftregister 1218 during a subsequent D-Capture operation. During eachD-Capture operation, the shift register 1218 and output circuit 1614both capture data. The shift register 1218 captures the present dataoutput from the output circuit 1614 and the output circuit 1614 capturesthe next data to be captured by the shift register during the nextD-Capture operation. Following the capture operation, the shift registershifts the data out to Out signal 120. As seen in this example, theD-Capture signal directly controls the output circuit 1614 to capturedata in response to the D-Clock signal.

In FIG. 16C, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1606 of datacircuit 1602 is realized as both a source output circuit 1614 forinputting data to the shift register 1218 via bus 1617 and as adestination input circuit 1612 for storing data output from the shiftregister 1218 via bus 1617. The destination input circuit 1612 andsource output circuit 1614 components of I/O circuit 1616 operate asdescribed in FIGS. 16A and 16B. In this example, the D-Capture signaldirectly controls the output circuit 1614 of I/O circuit 1616 to capturedata to be input to shift register 1218 in response to the D-Clocksignal, and the D-Update signal directly controls the input circuit 1612of I/O circuit 1616 to store data from shift register 1218.

In FIG. 16D, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1606 of datacircuit 1602 is realized as an destination input circuit 1618 forstoring the output from shift register 1218 via bus 1613. In thisexample, the input circuit 1618 is timed by a clock 1619 that is notsynchronized to the D-Clock signal. In order for the input circuit toknow when to store data from the shift register 1218 following a shiftin operation, an input sync circuit 1620 is required. The input synccircuit inputs the D-Update signal and the clock signal 1619, andoutputs an input enable signal 1621 to the input circuit. When theD-Update signal goes high at the end of a shift operation, the inputsync circuit synchronizes the D-Update signal with the clock signal 1619and outputs an input enable signal 1621 to the input circuit 1618. Inresponse to the input enable signal, the input circuit is enabled torespond to clock signal 1619 to store the data output from the shiftregister 1218 on bus 1613. The input sync circuit 1620 is designed tooutput one synchronized input enable signal to the input circuit foreach D-Update signal it receives, so only one data store occurs in inputcircuit 1618 for each occurrence of a D-Update signal. As seen in thisexample, the D-Update signal 520 indirectly controls the input circuit1618 to store data output from the shift register by synchronizing theD-Update signal with the clock signal 1619.

In FIG. 16E, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1606 of datacircuit 1602 is realized as a source output circuit 1622 for supplyingdata to the shift register 1218 via bus 1615. In this example, theoutput circuit 1622 is timed by a clock 1619 that is not synchronized tothe D-Clock signal. In order for the output circuit 1622 to know when tofetch the next input data to be stored in shift register 1218 after thepresent data has been captured into the shift register, an output synccircuit 1624 is required. The output sync circuit inputs the D-Capturesignal 518 and the clock signal 1619, and outputs an output enablesignal 1625 to the output circuit. When the D-Capture signal goes highduring a shift register 1218 capture operation, the output sync circuitsynchronizes the D-Capture signal with the clock signal 1619 and outputsan output enable signal 1625 to the output circuit 1622 when theD-Capture signal returns low. By waiting until the D-Capture signalreturns low to output the output enable signal 1625, the output circuit1622 is prevented from loading the next data to be input to the shiftregister 1218 until after the shift register has captured the presentdata being output from the output circuit 1622. Following the captureoperation, the data is shifted out of the shift register 1218 to the Outsignal 120. The output sync circuit 1624 is designed to output onesynchronized output enable signal 1625 to the output circuit for eachD-Capture signal it receives, so only one data load occurs in the outputcircuit 1624 for each occurrence of a D-Capture signal. As seen in thisexample, the D-Capture signal 518 indirectly controls the output circuit1622 to load data for input to the shift register by synchronizing theD-Capture signal with the clock signal 1619.

In FIG. 16F, the data register 1604 of data circuit 1602 is realized asthe shift register 1218 of FIG. 12, and the I/O circuit 1626 of datacircuit 1602 is realized as both a source output circuit 1622 forinputting data to the shift register 1218 via bus 1617 and as adestination input circuit 1618 for storing data output from the shiftregister 1218 via bus 1617. The destination input circuit 1618 andsource output circuit 1622 components of I/O circuit 1626 operate asdescribed in FIGS. 16D and 16E. To provide synchronization of theD-Update and D-Capture signals with the clock 1619 signal, an I/O synccircuit 1628 is provided. The I/O sync circuit 1628 incorporates boththe input sync circuit 1620 and the output sync circuit 1624. The inputsync circuit 1620 and output sync circuit 1624 components of I/O synccircuit 1628 operate as described in FIGS. 16D and 16E. In this example,the D-Capture signal indirectly controls the output circuit 1622 of I/Ocircuit 1626 to capture data to be input to shift register 1218 inresponse to the D-Clock signal, and the D-Update signal indirectlycontrols the input circuit 1618 of I/O circuit 1626 to store data fromshift register 1218.

FIG. 16G illustrates an example data circuit 1602 design for providingthe shift register 1218 of a data register 1604 to address one of fouraddressable I/O registers 1-4 existing as the general I/O circuitry ofFIG. 16 and write and/or read data to the addressed I/O register. Inthis example the bit pattern 1660 of the shift register 1218 ispartitioned into a first field 1662 for inputting and/or outputtingdata, a second field 1664 for outputting a write bit, and a third field1666 for outputting address bits. The write 1642 and address 1640 bitoutputs from the shift register 1218 are input to a register R/W controlcircuit 1638, along with the D-Update signal 520. The data output bits1644 from the shift register are input to the data inputs of the I/Oregisters 1-4 and the data input bits 1646 from the I/O registers 1-4are input to the shift register. The register R/W circuit 1638 controlsthe clocks (CK) and output enable (OE) inputs to the I/O registers 1-4.The register R/W circuit 1638 includes an address decode circuit 1648for inputting and decoding the address bit inputs (2 in this example)and outputting output enables signals 1-4 to the I/O registers 1-4,clock gating circuits 1652-1658 for inputting the output enable signals1-4 and the output of gate 1650 and outputting clock signal 1-4 to I/Oregisters 1-4. If the write bit is low (i.e. a read operation), gate1650 will not pass the D-Update signal to gates 1652-1658. If the writebit is high (i.e. a write operation), gate 1650 will pass the D-Updatesignal to gates 1652-1658.

During an I/O register write operation, the shift register 1218 isshifted to load the data to be written, to set the write bit high, andto set the address bits to select the I/O register to be written.Following the shift operation, the D-Update signal 520 from the messagecontroller 504 is activated which causes the addressed I/O register 1-4to be clocked via gating 1652-1658 to load the data from the shiftregister via bus 1644. During a following capture, shift, and updateoperation, the data output from the addressed I/O is enabled (OE1-4) andis captured into the shift register via bus 1646 and shifted out whilethe next pattern is shifted in. During the above mentioned capture step,the existing write bit 1642 and address bit 1640 values are re-capturedinto the shift register since they are fed back to the shift registerinputs. Data can be written to each of the other I/O registers 1-4 byrepeating the above capture, shift, and update operations to the shiftregister.

During an I/O register read operation, the shift register 1218 isshifted to set the write bit low and to set the address bits to selectthe I/O register to be read. Following the shift operation, the D-Updatesignal 520 from the message controller 504 is activated, but since thewrite bit is low no I/O register 1-4 clocks are output from gates1652-1658. During a following capture, shift, and update operation thedata output from the addressed I/O register is enabled (OE1-4) and iscaptured into the shift register via bus 1646 and shifted out while thenext pattern is shifted in. During the above mentioned capture step, theexisting write bit 1642 and address bit 1640 values are re-captured intothe shift register since they are fed back to the shift register inputs.Data from each of the other I/O registers 1-4 can be read by repeatingthe above capture, shift, and update operations to the shift register.

FIG. 17 illustrates an example of how the port and message resetcontroller 502 may be designed. The port and message reset controller502 consists of two separate controllers, a port reset controller 1720and a message reset controller 1722. The port reset controller 1720consists of inverters 1702 and 1705, Or gate 1704, and flip flop pairs1706 and 1708 connected as shown. Flip flop pairs 1706 and 1708 eachinclude a rising edge clock flip flop feeding data to a falling edgeflip flop, so it takes both a rising and falling clock edge to propagatean input to the pair to the output of the pair. The message resetcontroller 1722 consists of inverters 1710 and 1712, flip flop pairs1714 and 1716, and And gate 1718 connected as shown. Again the flip floppairs 1714 and 1716 include a rising edge clock flip flop feeding datato a falling edge clock flip flop. In response to a low input on thefunction reset input 134, flip flop pairs 1706 and 1708 are reset, whichsets the port reset output 132 low and the message reset output 508 low,via And gate 1718. In response to the function reset 134 returning high,the port reset controller 1720 will remain in the reset state (portreset 132 output low) if the clock signal 106 is high and the In signal118 is in a stable low or high state. The message reset controller flipflop pairs 1714 and 1716 are set while the clock signal is high.

During a message operation (i.e. an address and instruction message, oran address, instruction, and data message), the clock signal 106 isactive, forcing the flip flop pairs of the port and message controllerto be continuously forced to their set state due to the clock signal 106being coupled to the set (S) input of the pair's flip flops. In the setstate, the port and message controllers output highs on the port reset132 and message reset 508 outputs, respectively. At the end of messageoperations, the port and message reset controllers may be reset by aspecial sequence applied on the clock signal 106 and In signal 118 (viadata signal 104). The message reset controller 1722 is always resetfollowing a message so that a new message may be initiated. The messagereset output 508 of the message reset controller 1722 is used to forcethe message controller 504 of FIG. 5 to the shift address state 710 ofFIG. 7 so that the next message will start from that state. The portreset message controller 1720 is reset whenever all messages operationshave been performed and it is desired to force the 2 pin port into areset state. The port reset output 132 resets the instruction circuit112 to a known state and forces the message controller 504 to the shiftaddress state 710 via the message reset output 508. A low on the abovementioned function reset signal 134 does the same thing, i.e. forces themessage controller 504 to the shift address state 710 and initializesthe instruction circuit 112.

Timing diagram 1802 of FIG. 18 illustrates the above mentioned specialsequence applied on the clock 106 and In 118 signals which will resetthe port reset controller and output a low on the port reset 132 andmessage reset 508 signals. The sequence includes the steps of holdingthe clock signal 106 high while inputting a clock pulse or pulses on theIn signal 118. This port reset controller design example requires twoclock pulses on the In signal 118 due to the choice of using twoserially connected flip flop pairs 1706 and 1708. With clock signal 106high, the rising and falling edges of the first clock pulse on In signal118 sets the output of flip flop pair 1706 low (since clock signal 106is high) and the rising and falling edges of the second clock pulse onIn signal 118 sets the output of flip flop pair 1708 low, which forcesthe port reset 132 and message reset 508 signals low. The low on theport and message reset signals will be maintained until the clock signal106 goes low, which sets the outputs of flip flop pairs 1706 and 1708high and the port reset and message reset signals 132 and 508 high. Asindicated in dotted line, if desired, additional clock signals can occuron the In signal 118 after the port reset controller 1720 has receivedthe two clock pulses required to set the port reset signal 132 low.

Timing diagram 1804 of FIG. 18 illustrates the special sequence appliedon the clock 106 and In 118 signals which will reset the messagecontroller and output a low on the message reset 508 signal. Thesequence includes the steps of holding the clock signal 106 low andinputting two clock pulses on the In signal 118. Like the port resetcontroller design example 1720 above, the message reset controllerdesign example 1722 uses two serially connected flip flop pairs 1714 and1716 for use with two clock pulses on the In signal 118. With clocksignal 106 low, the rising and falling edges of the first clock pulse onIn signal 118 sets the output of flip flop pair 1714 low and the risingand falling edges of the second clock pulse on In signal 118 sets theoutput of flip flop pair 1716 low, which forces the message reset 508signal low. The low on the message reset signal will be maintained untilthe clock signal 106 goes high, which sets the outputs flip flop pairs1714 and 1716 high and the message reset signal 508 high. As indicatedin dotted line, if desired, additional clock signals can occur on the Insignal 118 after the message reset controller 1722 has received the twoclock pulses required to set the message reset signal 508 low.

While two clock pulses on In 118 and two flip flop pairs were used inthe design examples of the port and reset controllers 1720 and 1722above, a lesser or greater number of clock pulses and flip flop pairsmay be used as well. A flip flop pair is required for each clock pulseused in the special sequence. The use of two clock pulses on In 118 andtwo flip flop pairs were used in these examples because it reduces theprobability that noise or signal skew problems might produce the specialsequences on clock 106 and In 118 during message operations that wouldforce the port and message reset controllers to inadvertently entertheir reset states and output lows on the port and message reset signals132 and 508. The special port and message reset signaling sequencesshown in the timing diagrams 1802 and 1804 of FIG. 18 are sequences thatare never produced on the clock signal 106 and In signal 118 duringmessage operations. These special sequences, when output by the 2 pinbus controller 302, are only detectable by the port reset 1720 andmessage reset 1722 controllers of the 2 pin bus target.

FIG. 19 illustrates the timing on the clock 106 and data 104 signals tooperate the port of a target to perform an address and instructionmessage operation. The timing displays the clock and data signals asthey would appear on the clock and data wiring (or other forms of signalconnections) between a port controller 302 and a target port 310, 312,314. The target port states relate to the message controller statediagram of FIG. 7. Initially the target port of FIG. 19 is in themessage reset state 706 with the clock signal wire low and pulses on thedata signal wire. When the clock goes high, the port exits the messagereset state 706 and removes the message reset condition (signal 508) onthe message controller 504. With the message reset condition removed,the message controller 504 is enabled in the shift address state 710 andready to shift in address data. When the clock returns low at 1902, theport controller outputs the first address data bit onto the data signalwire. The following rising edge of the clock at 1904 clocks the firstaddress bit into the address circuit 110.

During the shift address state 710, additional address bits are outputfrom the controller on the falling edge of the clock and shifted intothe address circuit 110 on the rising edge of the clock up to andincluding the last address bit on rising clock edge 1906. On rising edge1908, the message controller evaluates the address for a match inaddress match state 712. During rising edge 1908, the value on the datawire is a don't care as indicated in FIGS. 19 and 20 by slash lines. Itis assumed the address matches, so the message controller enters theshift instruction state 714.

On rising edge 1912, the message controller shifts in the firstinstruction bit from the port controller to the instruction circuit 112.The instruction bit shift in operation continues until the lastinstruction bit is shifted into the instruction circuit on the risingclock edge 1914. On falling clock edge 1915, the port controller setsthe data wire low to prepare for issuing the special clock and datasequence to return to the message reset state 706 at time 1920. Onrising clock edge 1916, the message controller updates the instructioncircuit outputs in update instruction state 716 to enable theinstruction. The port controller sets the clock wire low at 1918.

At time 1920, the port controller issues the special sequence on theclock and data wire to cause the target port to return to the messagereset state 706, which resets the message controller 504 and terminatesthe address and instruction message operation. The above describedaddress and instruction message operation can be repeated as needed toindividually address and input instructions to target ports. If theaddress shifted in is the global port address mentioned in regard toFIGS. 3 and 10, all target ports will be addressed to input and updatethe instruction.

FIG. 20 illustrates the timing on the clock 106 and data 104 signals tooperate the port of a target to perform an address, instruction and datamessage operation. From the message reset state 706 to the updateinstruction state 716, the address and instruction timing occurs asdescribed above in FIG. 19. Since data is to be communicated followingthe update of the instruction, the port controller does not issue thespecial sequence to enter the message reset state 706 as it did in FIG.19, but rather continues to operate the data and clock signal wiresfollowing update instruction state 716.

During the capture data state 718 parallel data to be sent to the portcontroller via the data signal wire 104 is captured into the datacircuit 1212 selected by the instruction on rising clock edge 2002.During the falling clock edge 2004 of the shift data state 720 theoutput enable signal 416 from message controller 504 goes high, as shownin FIG. 8. The high on output enable signal 416 causes the data I/Ocircuit 402 to switch from being a unidirectional data input circuit tobeing a bidirectional data input and output circuit, as described inFIGS. 4, 7, and 8.

The details of how the data I/O circuit operates to simultaneously inputand output data on the data signal wire 104 will be described in detaillater in regard to FIGS. 25-28. For now, let it simply be said that whenboth the port controller and the target port are outputting the samelogic level voltages, high or low, the wire will be set to that logiclevel voltage, and when the port controller and target port areoutputting opposite logic level voltages the wire will be set to avoltage that lies between the opposite logic level voltages, say amiddle (mid) voltage.

On the falling clock edge 2004 of the shift data state 720 both the portcontroller and target port output first data signals onto data signalwire 104. As seen, the first data signal 2012 on the data wire is eitherhigh or low, which means that the data signals output from the portcontroller and target port or both either high or low, respectively. Onrising clock edge 2006 both the port controller and the target portinput the data signal 2012. The data signal 2012 indicates, by virtue ofits logic level, the data being output from the port controller to thetarget port and the data being output from the target port to the portcontroller. On the falling clock edge 2008, the port controller andtarget port output second data signals onto data signal wire 104.

As seen, the second data signal 2014 on the data wire is at a midvoltage, which means that the data signals output from the portcontroller and target port are at opposite logic levels. On the risingclock edge 2010, the port controller and the target port input databased on the mid point voltage signal 2014 and the data each wasattempting to output.

For example if the target port was outputting a logic high and the wireis at a mid point voltage, the target port will know that the portcontroller was outputting a logic zero, which caused the wire to be at amid point voltage, and will input a logic zero to the selected datacircuit 1212 on rising clock edge 2010. Similarly, if the portcontroller is outputting a logic low and the wire is at a mid pointvoltage, the port controller will know that the target port wasoutputting a logic high and will input a logic high. The bidirectionaldata transfer between the port controller and the target port continueswhile the target port is in the shift data state 720. On rising clockedge 2016 the last data is transferred between the port controller andthe target port and the message controller 504 of the target port entersthe update data state 722. In the update data state, the output enablesignal 416 from the message controller 504 to the data I/O circuit 402is set low to cause the data I/O circuit to switch from operating in thebidirectional data transfer mode to the unidirectional input mode. Onrising edge 2018 of the update data state 722 the data shifted into theselected data circuit 1212 is updated to the data circuit's paralleloutputs.

The sequence from the rising clock edge 2002 to the rising clock edge2018 defines the first capture (1), shift (1), and update (1) operationsof the first data frame transferred between the port controller and thetarget port. Additional data frames may follow the first data frame. Thesequence from the rising clock edge 2020 to the rising clock edge 2024defines the last capture (N), shift (N), and update (N) operations ofthe last data frame transferred between the port controller and thetarget port. After the last data frame (N) is transferred, the portcontroller sets the data signal wire low on falling edge 2022 and setsthe clock wire low at 2026. At time 2028, the port controller issues thespecial sequence on the clock and data wire to cause the target port toreturn to the message reset state 706, which resets the messagecontroller 504 and terminates the address, instruction, and data messageoperation. The above described address, instruction, and data messageoperation can be repeated as needed to individually address a targetport, input an instruction to the target port, and perform a data I/Ooperation to the target port.

FIG. 21 illustrates a timing diagram depicting the end of a messageframe, the issuance of a message reset sequence, and the start of a newmessage frame.

FIG. 22 illustrates a timing diagram depicting the end of a messageframe, the issuance of a message reset sequence, the issuance of a portreset sequence, and the issuance of a message reset sequence.

FIG. 23 illustrates a timing diagram depicting the end of a messageframe, the issuance of a message reset sequence, the issuance of a portreset sequence, and the issuance of a pre-port disconnect sequence. Thepre-port disconnect sequence is used to set the clock 106 and data 104signals high prior to disconnecting the port controller from the targetport. The clock and data signals will remain high when the portcontroller is disconnected by the pull up elements 116 shown in FIG. 1.

FIG. 24 illustrates a timing diagram depicting the end of a messageframe, the issuance of a port reset sequence, and the issuance of apre-port disconnect sequence. This timing diagram indicates that theport reset sequence may be issued immediately following a message frameif desired.

While the timing diagrams in FIGS. 19-24 have shown the port controllerand target port inputting data from the data signal wire on one edge ofclock signal 106 and outputting data to the data signal wire on theopposite edge of clock signal 106, it should be understood that the portcontroller and target ports could be designed to input and output dataon the same clock edge if desired. Also, while the certain static logiclevels were used on the clock signal 106 during the special sequencesfor message reset (clock=low) and port reset (clock=high), the specialsequences may be defined using opposite static logic levels on the clocksignal as well.

FIG. 25 illustrates the data signal wire connection 2506 between thedata I/O circuit 2510 of a port controller 302 and data I/O circuits 402of 1-N target circuits 310. Preferably, the output buffer 2508 of theport controller data I/O circuit 2510 and the output buffers 406 of thetarget circuit data I/O circuits 402 will have approximately the samecurrent sink/source drive strength. Also preferably the resistors 404 ofthe port controller and target circuit data I/O circuits will haveapproximately the same resistance. As seen the output buffer 2508 of theport controller's data I/O circuit is always enabled to output data tothe target ports, while the output buffers 406 of the target port dataI/O circuits are selectively enabled and disabled by the output enablesignal 416 from the message controller 504. The In1-In N signals 118 ofthe target port data I/O circuit 402 are coupled to the serial datainputs of the target port's address 110, instruction 112, and data 114circuits as previously described. The Out1-Out N signals 120 of thetarget port data I/O circuit 402 are coupled to the serial data outputof the data circuits 114 as previously described. The In signal 2502 ofthe port controller's data I/O circuit 2510 is coupled to a circuitwithin the port controller designed to receive serial data input signalsfrom data signal wired 2506, and the Out signal 2504 of the portcontroller's data I/O circuit 2510 is coupled to a circuit within theport controller designed to transmit serial data output signals to datasignal wire 2506.

During address and instruction shift operations, the output buffers 406of the target circuits 310 are disabled, providing the output buffer2506 of the port controller to be the sole driver of the data signalwire 2506. During address shift operations, the input circuit 408 of thetarget circuits operates as an input buffer to pass the address datafrom the port controller to the In1-N signals 118. During instructionshift operations, the input circuit 408 of the addressed target circuitcontinues to operate as an input buffer to pass instruction data fromthe port controller to the In1-N signals 118.

During data shift operations, the output buffer 406 of the selected(addressed) target circuit is enabled via the output enable signal 416,providing both the output buffer 2506 of the port controller and theoutput buffer 406 of the selected target port to source data onto datasignal wire 2506. If the port controller output buffer 2508 and targetport output buffer 406 both output the same logic level to the datasignal wire 2506, the data signal wire will be at that logic level. Ifthe port controller output buffer 2508 and the target port output buffer406 output opposite logic levels, the data signal wire will be at a midpoint voltage level between the two opposite logic levels. When theoutput buffers 2508 and 406 are driving the data signal wire 2506 withopposite logic levels, the resistors 404 serve to limit the current flowbetween the two output buffers and serve as voltage droppers to providethe mid point voltage level on data signal wire 2506 to be more easilydetected by the data input circuits 408 as a voltage level that isdistinctly different than the normal logic level voltage level outputfrom the output buffers 2506 and 406.

FIG. 26 illustrates one example of how to design the data input circuit408 of the data I/O circuits 2510 and 402. The data input circuit 408includes a voltage comparator circuit 2606, multiplexer 2608, aninverter 2604, and a buffer 2602. The voltage comparator circuit 2606inputs voltages from the data wire signal 2506 via connection 412 andoutputs digital control signals S0 and S1 to multiplexer 2608. As seen,the first voltage (V) to ground (G) leg 2618 of voltage comparatorcircuit 2606 comprises a series P-channel transistor and current sourceand the second voltage to ground leg 2620 comprises a series N-channeltransistor and current source. As seen, S1 is connected at a pointbetween the P-channel transistor and current source of the first leg2618 and S0 is connected at a point between the N-channel transistor andcurrent source of the second leg 2620. The gates of the transistors areconnected to wire input connection 412 to provide voltages on the datasignal wire 2506 to turn the transistors on and off.

The operation of the voltage comparator circuit 2606 and multiplexer2608 is shown in table 2610 and is described herein. If the voltage onwire connection 412 is at a low level (logic zero), the S0 and S1outputs are set high, which causes the multplexer 2608 to select its lowinput 2612 and output the low input to In 118 via connection 2618 andbuffer 2602. If the voltage on wire connection 412 is at a mid level(mid point voltage), the S0 is set low and the S1 is set high, whichcauses the multplexer 2608 to select its Out* input 2614 (inverted Outsignal 120) and output the Out* input to In 118 via connection 2618 andbuffer 2602. If the voltage on wire connection 412 is high (logic one),the S0 and S1 outputs are set low, which causes the multiplexer 2608 toselect its high input 2616 and output the high input to In 118 viaconnection 2618 and buffer 2602.

FIG. 27A illustrates the case where the port controller output buffer2508 and target port output buffer 406 are both outputting logic lows todata signal wire 2506. In this case the data signal wire is low and thewire 412 input to the data input circuits 408 of the port controller andtarget port is low. This causes; (1) the data input circuit 408 of theport controller to input a low to the port controller on In signal 2502and (2) the data input circuit 408 of the target port to input a low tothe target port on In signal 118.

FIG. 27B illustrates the case where the port controller output buffer2508 is outputting a low on data signal wire 2506 and target port outputbuffer 406 is outputting a high on data signal wire 2506. In this case acurrent path exists from the high voltage output (V) from buffer 406 tothe low voltage output (G) from buffer 2508. The resistors 404 limit thecurrent flow and the voltage drops across them produce a distinctlydetectable mid point voltage level on the data signal wire 2506. The midpoint voltage level on the data signal wire is input to the data inputcircuits 408 of the port controller and target port, via connections412. Since the data input circuit 408 of the port controller knows theport controller was outputting a logic low, it responds to the mid pointvoltage by inputting a logic high to the port controller on In signal2502, which is the only voltage that can be output from the target portbuffer 406 to cause the mid point voltage on data signal wire 2506.Similarly, since the data input circuit 408 of the target port knows thetarget port was outputting a logic high, it responds to the mid pointvoltage by inputting a logic low to the target port on In signal 118,which is the only voltage that can be output from the port controllerbuffer 2508 to cause the mid point voltage on data signal wire 2506.

FIG. 27C illustrates the case where the port controller output buffer2508 is outputting a high on data signal wire 2506 and target portoutput buffer 406 is outputting a low on data signal wire 2506. In thiscase a current path exists from the high voltage output (V) from buffer2508 to the low voltage output (G) from buffer 406. Again, the resistors404 limit the current flow and the voltage drops across them produce adistinctly detectable mid point voltage level on the data signal wire2506. The mid point voltage level on the data signal wire is input tothe data input circuits 408 of the port controller and target port, viaconnections 412. Since the data input circuit 408 of the target portknows the target port was outputting a logic low, it responds to the midpoint voltage by inputting a logic high on In signal 118 to the targetport, which is the only voltage that can be output from the portcontroller buffer 2506 to cause the mid point voltage on data signalwire 2506. Similarly, since the data input circuit 408 of the portcontroller knows the port controller was outputting a logic high, itresponds to the mid point voltage by inputting a logic low to the portcontroller on In signal 2502, which is the only voltage that can beoutput from the target port buffer 406 to cause the mid point voltage ondata signal wire 2506.

FIG. 27D illustrates the case where the port controller output buffer2508 and target port output buffer 406 are both outputting logic highsto data signal wire 2506. In this case the data signal wire is high andthe wire 412 input to the data input circuits 408 of the port controllerand target port is high. This causes; (1) the data input circuit 408 ofthe port controller to input a high to the port controller on In signal2502 and (2) the data input circuit 408 of the target port to input ahigh to the target port on In signal 118.

FIG. 28 illustrates timing waveforms 2802 for the four cases (A,B,C,D)in which simultaneous data communication occurs between a portcontroller 302 and a selected (output enable signal is high) target port310, via data signal wire 2506. Each case A-D is indicated in the timingdiagram by vertical dotted line boxes.

FIG. 29 illustrates how the 2 pin port in a device (IC or core) 2902 maybe extended to include auxiliary data signals 2904-2908 to increase thedata input and output bandwidth between the device 2902 and an externalport controller 2901. For simplification, the address 110 andinstruction 112 circuits are not shown in FIG. 29. As seen, the deviceincludes the 2 pin port 108 which includes the data I/O port 402 and theport controller 418. The external port controller 2901 is connected tothe 2 pin port's data I/O port 402 via data signal 104 and to the 2 pinport's controller 418 via the clock signal 106 as previously described.The device includes auxiliary data I/O circuits (402) 2912-2916, one foreach auxiliary data signal 2904-2908. The external controller 2901 isconnected to each auxiliary data I/O circuit 2912-2916 via an auxiliarydata signal 2904-2908. The external controller 2901 includes a data I/Ocircuit 2510 for each auxiliary data signal 2904-2908 to providebidirectional data communication to the auxiliary data I/O circuits2912-2916 of device 2902 as described in FIGS. 25-28 for the data signal104.

The 2 pin port may operate with the external controller 2901 using onlythe clock 106 and data 104 signals as previously described, or it mayoperate with the external controller 2901 using the clock 106, data 104,and auxiliary data signals 2904-2908. The instruction shifted into theinstruction circuit 112 (not shown) will determine whether the 2 pinport operates in single data I/O mode using only data signal 104 oroperates in parallel data I/O mode using data signal 104 and theauxiliary data signals 2904-2908. As can be understood, the paralleldata I/O mode significantly increases the data bandwidth between thedevice 2902 and controller 2901 over that possible in the single dataI/O mode.

When operating in the parallel data I/O mode, the data I/O circuits 402and 2912-2916 of the data signal 104 and auxiliary data signals2904-2908 are coupled, in response to an instruction, to selected datacircuits (1212) 2918-2924, such that the data circuits may input datafrom the In signal output of the data I/O circuits and output data tothe Out signal input of the data I/O circuits. While not shown, theoutput data from the data circuits 2918-2924 to the Out signal input ofthe data I/O circuits 402 and 2912-2916 will be timed on the fallingedge of the clock 106 signal by a flip flop (like flip flop 1312) asdescribed in FIG. 13.

During parallel data I/O mode, the data I/O circuit 402 is enabled bythe output enable signal 416 of port controller 418, the data I/Ocircuits 2912-2916 are enabled by the output enable signal 416A from Andgate 2936, and the data circuits 2918-2924 are controlled to capture,shift, and update by appropriate D-Capture 518, D-Clock 516, andD-Update 520 control signals on DC bus 130. During the parallel data I/Omode, the data circuits 2918-2924 will be controlled by the portcontroller 418 to capture data in the capture state 718, shift data inthe shift state 720, and update data in the update state 722. The dataappearing on the wiring of the data signal 104 and auxiliary datasignals 2904-2908 between controller 2901 and device 2902 during thedata capture, shift, and update operations is the same as shown in thetiming diagram of FIG. 20. This capture, shift, and update sequence arerepeated as necessary to perform a parallel data I/O operation betweenthe controller 2901 and device 2902. As previously described, the clocksignal 106 and data signal 104 are used to issue the message resetsequence to the port controller 418 which terminates the parallel dataI/O operation mode.

The auxiliary data signals 2904-2908 of a device may be dedicatedsignals or they may be signals shared with other signals of the device,such as functional signals. For example in an IC or core device, theauxiliary data signals 2904-2908 of data I/O circuits 2912-2916 may havetheir own dedicated external device terminals or the auxiliary datasignals of the data I/O circuits may share external device terminalswith other circuits 2930-2934 using the terminals for input, output, orI/O operations.

If the device terminals are shared, a parallel mode enable (PME) signal2938 from instruction output bus 128 determines whether the terminalsare used by the data I/O circuits 2912-2916 or by the other circuits2932-2934. If the output terminals are to be used by the other circuits,an instruction will be loaded that sets the PME signal 2938 low, whichenables the other circuits to use the terminals and forces the outputenable signal 416A from And gate 2938 low. While PME is low, the outputenable signal 416 from the port controller 418 can enable data I/Ocircuit 402 to operate in the bidirectional data mode, but cannot enabledata I/O circuits 2912-2916 to operate in the bidirectional data mode,i.e. data I/O circuits 2912-2916 remain in the input only mode. If theoutput terminals are to be used by the data I/O circuits 2912-2916, aninstruction will be loaded that sets the PME signal 2938 high, whichdisables the other circuits 2932-2934 from using the terminals andenables the output enable signal 416A to be driven by the output enablesignal 416 from the port controller 418. With output enable signal 416driving output enable signal 416A the data I/O circuits 2912-2916operate in the bidirectional data mode whenever data I/O circuit 402operates in the bidirectional data mode.

From the above it is seen that when the PME signal 2938 is low, thedevice communicates data to and from the controller 2901 using only theclock 106 and data 104 signals, but when the PME signal 2938 is high,the device communicates data to and from the controller 2901 using theclock 106, data 104, and auxiliary data 2904-2908 signals. Thus the PMEsignal selectively enables either single or parallel data I/O modes ofthe present invention. If it is determined that only parallel data I/Omodes are used and the device terminals are dedicated for use only bythe auxiliary data signals 2904-2908 only, the PME signal 2938 and Andgate 2936 can be eliminated from FIG. 29 and the output enable signal416 from port controller 418 can be directly connected to signal 416A.This provides data I/O circuit 402 and data I/O circuits 2912-2916 toalways operate together during bidirectional data I/O operations.

FIG. 30 illustrates the IC or core device 2902 wherein the data circuits(1212) 3002-3008 selected by an instruction for a parallel data I/Ooperation are scan registers 1-N used for testing. The scan registers1-N could be the internal scan registers 1404 of FIG. 14, the boundaryscan registers 1504 of FIG. 15, or a combination of internal scanregisters 1404 and boundary scan registers 1504. An important scan testimprovement, enabled by the present invention and shown in FIG. 30, isthat during scan testing each scan register 3002-3008 inputs teststimulus data from the port controller 2901 and outputs test responsedata to port controller 2901, via a single data signal wire 104,2904-2908. Conventional device (IC or core) scan registers require twodata signal wires for scan testing, a first signal wire for inputtingtest stimulus data from the tester (port controller 2901) and a secondsignal wire for outputting test response data to the tester. Thus thepresent invention provides the advantage of performing scan data inputand output to the scan registers of a device using only one data wireper scan register. This advantageously reduces the number of connectionsbetween a device under test and the tester.

FIG. 31 illustrates the IC or core device 2902 wherein the data circuits3002-3008 of FIG. 30 selected by an instruction for a parallel data I/Ooperation are circuits 3102-3108 1-N used for debug or trace operations.Debug circuits are internal circuits of a device used to detectoperational problems in the device's functional hardware or softwaredesign. Trace circuits are internal circuits of a device used to monitorthe signal activity of the device during its normal operation mode. Aswith the scan register example of FIG. 30, the present invention enablesdata access to each debug or trace circuit 1-N using only a single datasignal 104, 2904-2908, which advantageously reduces the number ofconnections required between the debug/trace controller (port controller2901) and the device.

FIG. 32 illustrates the IC or core device 2902 wherein the data circuits3202-3208 selected by an instruction for a parallel data I/O operationare functional circuits 1-N of the device. The function circuits utilizethe parallel data I/O operation for communicating functional data to andfrom a functional I/O controller (port controller 2901). As with theexamples of FIGS. 30 and 31, the present invention enables data accessto each functional circuit 1-N using only a single data signal 104,2904-2908, which advantageously reduces the number of functionalconnections required between the functional controller and the device.

I claim:
 1. An integrated circuit comprising: (a) a bidirectional datapin; (b) a clock input pin; (c) shift register circuitry having a datainput coupled to the bidirectional data pin, a data output coupled tothe bidirectional data pin, a clock input coupled to the clock inputpin, data bit outputs, address bit outputs, and a write bit output; and(d) a target circuit including: (i) a first data register having a firstenable input and inputs coupled to the data bit outputs and the writebit output; (ii) a second data register having a second enable input andinputs coupled to the data bit outputs and the write bit output; and(iii) address decode circuitry having inputs coupled to the address bitoutputs, and having a first enable output coupled to the first enableinput and a second enable output coupled to the second enable input,wherein the first data register and the second data register selected bythe address bit outputs are operable to be written with the data bitoutputs when the write bit output is a first value and to be read whenthe write bit output is a second value.
 2. The integrated circuit ofclaim 1 in which the target circuit is I/O circuitry.
 3. The integratedcircuit of claim 1 in which the target circuit is Scan circuitry.
 4. Theintegrated circuit of claim 1 in which the target circuit is Tracecircuitry.
 5. The integrated circuit of claim 1 in which the targetcircuit is functional circuitry.
 6. The integrated circuit of claim 1further including: (a) second shift register circuitry having a datainput coupled to the bidirectional data pin, a data output coupled tothe bidirectional data pin, a clock input coupled to the clock inputpin, second data bit outputs, second address bit outputs, and a secondwrite bit output; and (b) a second target circuit including: (i) a thirddata register having a third enable input and inputs coupled to thesecond data bit outputs and the second write bit output; (ii) a fourthdata register having a fourth enable input and inputs coupled to thesecond data bit outputs and the second write bit output; and (iii)second address decode circuitry having inputs coupled to the secondaddress bit outputs, and having a third enable output coupled to thethird enable input and a fourth enable output coupled to the fourthenable input, wherein the third data register and the fourth dataregister selected by the second address bit outputs are operable to bewritten with the second data bit outputs when the second write bitoutput is a first value and to be read when the second write bit outputis a second value.
 7. The integrated circuit of claim 6 furtherincluding a multiplexer having a first input coupled to the data outputof the shift register circuitry, a second input coupled to the dataoutput of the second shift register circuitry, and an output coupled tothe bidirectional data pin.
 8. The integrated circuit of claim 1 inwhich the shift register circuitry includes a data bit register havingan input coupled to the bidirectional data pin and outputs coupled tothe data bit outputs.
 9. The integrated circuit of claim 1 in which theshift register circuitry includes an address register having an inputcoupled to the bidirectional data pin and outputs coupled to the addressbit outputs.
 10. The integrated circuit of claim 1 in which the shiftregister circuitry includes a write bit register having an input coupledto the bidirectional data pin and an output coupled to the write bitoutput.